Variable-speed pumped storage generator-motors employ fractional pole-count ratio windings in the stator to address mismatches in rotational speed, capacity, and terminal voltage. However, this can lead to asymmetric magnetomotive forces among parallel branches and generate circulating currents, which affect the electromagnetic force and vibration characteristics. To investigate the impact of branch circulating currents on electromagnetic forces and vibrations in variable-speed pumped storage generator-motors with fractional pole-count ratio windings, analytical models for the stator magnetomotive force and electromagnetic forces considering circulating currents were derived. Finite element analysis was used to examine the characteristics of electromagnetic forces under two scenarios: neglecting and accounting for circulating currents. Further analysis was conducted on the variation characteristics of unbalanced magnetic pull. The results from harmonic response analysis of electromagnetic vibrations align well with the analytical findings. Vibration data from actual machine tests also confirm that circulating currents influence low-frequency vibrations. Vibration data from prototype tests indicate that branch circulating currents increase the fundamental low-frequency vibration and 4th-harmonic vibration, while slightly reducing the 6th-harmonic vibration, verifying the theoretical analysis and finite element model. The findings offer insights for mitigating vibration and improving the operational stability and reliability of variable-speed pumped storage generator-motors.